It may seem like common sense that keeping smartphones away from kids would improve their performance at school. Now a study by the London School of Economics has the data to back it up.

The study looked at 91 schools across the U.K. and focused specifically on the national exams 16-year-old students take. Kids who went to schools that ban smartphones saw an average 6.4% test score improvement across the board, and this effect was even greater for underachieving students -- those in the "lowest quartile of prior achievement," according to the study. These kids saw that average rise by a whopping 14%.

"By surveying schools in four English cities regarding their mobile phone policies and combining it with administrative data, we find that student performance in high stakes exams significantly increases post ban," authors Louis-Philippe Beland and Richard Murphy wrote in the study's abstract. "Our results indicate that these increases in performance are driven by the lowest-achieving students."

Test score requirements and tight budgets are frequently top of mind for U.S. schools, and these researchers cite cell phone bans as "a low-cost policy to reduce educational inequalities."

"We found the impact of banning phones for these students equivalent to an additional hour a week in school, or to increasing the school year by five days," the study says.

This particular study runs counter to a recent decision by New York City Mayor Bill de Blasio, who gave schools the right to make their own rules regarding smartphones earlier this year.

So, shocker, keeping students off Candy Crush during school hours makes for better math grades. Let's just hope it fuels a decline in selfie stick usage, too.